Furnace Not Heating? 6 Parts to Check Before Calling a Pro
Your furnace stopped heating and the house is getting cold. Before you spend $300–$800 on a service call, here are six parts you can check and replace yourself — in order from most common to least common failure. Most of these are under $70 and take less than 30 minutes to swap.
We sell all of these at Open To Public HVAC Parts in Dallas, and we’ll test suspect parts at the counter for free.
First: Check the Simple Stuff
Before you open anything, rule out the basics:
- Thermostat — Is it set to HEAT? Is the temperature set above room temp? Try bumping it up 5 degrees.
- Breaker — Check the breaker panel. Furnace breakers trip sometimes, especially after a power outage.
- Gas supply — Is the gas valve on the supply line open? It’s a lever near the furnace — parallel to the pipe means open, perpendicular means closed.
- Filter — A severely clogged filter can cause the furnace to overheat and shut down. Pull it out and check.
If all that’s fine and the furnace still won’t heat, it’s time to look at parts. Here’s what fails most often.
1. Hot Surface Ignitor — The Most Common Furnace Failure
What happens: The inducer motor starts (you hear a whirring noise), the gas valve clicks, but the burners never light. The ignitor should glow bright orange — if it doesn’t, it’s dead.
Why it fails: Ignitors are fragile ceramic elements that crack or weaken over time. They’re the most-replaced furnace part by a wide margin.
DIY cost: $30–$70
Pro cost: $200–$400
Difficulty: Easy — one screw, one wire connector, 5 minutes.
Read our full guide: Where to Buy a Furnace Ignitor in Dallas
2. Flame Sensor — Lights Then Shuts Off
What happens: The burners light, flame appears, then the furnace shuts off after 3–5 seconds. Repeats 2–3 times then locks out.
Why it fails: The flame sensor is a small metal rod that sits in the burner flame. It tells the control board that gas is actually burning. When it gets coated with carbon or oxidation, it can’t sense the flame and the board shuts off the gas as a safety measure.
DIY cost: $15–$30 (or free if cleaning fixes it)
Pro cost: $150–$300
Difficulty: Very easy — one screw, pull it out, clean with steel wool or replace.
Pro Tip: Before buying a new one, try cleaning the existing sensor rod with fine steel wool or even a dollar bill. Rub the metal rod until it’s shiny. That fixes the problem about half the time.
→ Browse flame sensors in stock
3. Pressure Switch — Inducer Runs But Nothing Else Happens
What happens: The inducer motor starts and runs, but the ignition sequence never begins. No click from the gas valve, no glow from the ignitor. The furnace just sits there with the inducer running.
Why it fails: The pressure switch confirms that the inducer motor is pulling exhaust gases out of the heat exchanger. If the switch doesn’t close, the control board won’t allow ignition. The switch itself can fail, or the rubber hose connecting it to the inducer can crack or clog.
DIY cost: $20–$45
Pro cost: $150–$300
Difficulty: Easy — one or two wires, one hose, usually snaps in place.
Pro Tip: Before replacing the switch, check the rubber hose that connects to it. If it’s cracked, kinked, or full of water, that’s your problem — not the switch.
Read our Furnace Short Cycling Guide — pressure switch issues often cause short cycling.
→ Browse pressure switches in stock
4. Inducer Motor — No Sound at All When Furnace Tries to Start
What happens: The thermostat calls for heat but nothing happens. No sound from the furnace at all, or you hear a humming/buzzing but the inducer fan doesn’t spin.
Why it fails: The inducer motor is the first thing that runs in the ignition sequence. It pulls combustion gases through the heat exchanger and out the flue. When it fails, the entire ignition sequence is blocked.
DIY cost: $100–$250
Pro cost: $400–$800
Difficulty: Moderate — 3–4 screws, a wiring harness, and a flue connection. 30–60 minutes.
Important: Inducer motors are model-specific. Bring your furnace model number or the old motor — we’ll cross-reference the exact replacement.
→ Browse inducer motors in stock
5. Gas Valve — No Click, No Gas
What happens: The inducer motor runs, the pressure switch closes, the ignitor glows — but you never hear the click of the gas valve opening. No gas reaches the burners.
Why it fails: The gas valve is an electrically controlled valve that opens to allow gas flow to the burners. The solenoid inside can fail, or the valve can stick closed.
DIY cost: $80–$150
Pro cost: $300–$600
Difficulty: Moderate — involves disconnecting gas lines. If you’re not comfortable working with gas connections, this is one to have a pro do.
Pro Tip: Before replacing the gas valve, make sure the ignitor is actually getting hot and the control board is sending voltage to the valve. A bad board or wiring issue can mimic a gas valve failure.
6. Control Board — The Brain of the Furnace
What happens: Erratic behavior — the furnace might try to start and fail in unusual patterns, or multiple components seem to not work correctly. LED error codes flash on the board.
Why it fails: The control board manages the entire ignition sequence: inducer → pressure switch → ignitor → gas valve → flame sensor → blower. If the board’s relays or circuits fail, any part of that sequence can break down.
DIY cost: $80–$180
Pro cost: $300–$700
Difficulty: Moderate — multiple wire connections, but it’s essentially unplugging the old board and plugging in the new one. Take a photo of all wiring before disconnecting.
Pro Tip: Check the LED blink codes on the board — there’s usually a legend on the inside of the furnace door that tells you what each pattern means. That code often points to a specific component failure, not the board itself.
→ Browse control boards in stock
The Ignition Sequence — Understanding What Happens When
Knowing the order of operations helps you diagnose where the failure is:
- Thermostat calls for heat
- Inducer motor starts (pulls exhaust out)
- Pressure switch closes (confirms airflow)
- Ignitor heats up (glows orange)
- Gas valve opens (gas flows to burners)
- Burners ignite
- Flame sensor confirms flame is present
- Blower motor starts after a short delay (pushes warm air through ducts)
If the furnace stops at any step, the part responsible for that step is where you start looking. For example: if you hear the inducer but nothing else, the pressure switch is step 3. If the ignitor glows but no flame appears, the gas valve is step 5.
For a complete walkthrough, see our Furnace Not Heating Troubleshooting Guide.
Bring It In — We’ll Test It Free
Not sure which part failed? Pull the suspect part out and bring it to our counter. We test ignitors, flame sensors, pressure switches, capacitors, and more — for free. We’d rather test it and tell you it’s good than sell you something you don’t need.
Open To Public HVAC Parts
10226 Plano Rd, Suite 104, Dallas, TX 75238
(214) 340-9421 — call or text
Mon–Fri 10am–7pm | Sat 10am–3pm
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